Lama Atisha explained why reciting the names of the Thirty-five Buddhas has so much power. In the past, when the Thirty-five Buddhas were Bodhisattvas, they made many prayers to be able to benefit sentient beings, to easily purify our defilement's and negative karma. When they achieved enlightenment, they achieved the Buddha’s ten qualities or powers, one of which is the power of prayer. So, their names have the power of all those past prayers. That is why, when sentient beings recite their names, they have so much power to purify defilement's and eons of negative karma. Every single quality the Thirty-five Buddhas attained was in order to benefit sentient beings, there was no other reason or motivation for it, so we should use this advantage.